For prevention and early detection of construction machine thefts which lately take place at an increasing frequency particularly for construction machines such as hydraulic power shovels, hydraulic cranes, bulldozer and the like, there has been proposed to establish a construction machine management center for surveillance of locations of construction machines, for example, as in Japanese Laid-Open Patent Application 2000-73411. According to this prior art, the position of a construction machine on a working site is measured on the basis of GPS (Global Positioning System) signals, using the resulting position data for judging possibilities of a machine theft. Namely, in this case, a place or an area where a construction machine is normally supposed to be located is set up as a proper working area in a management server of the construction machine management center. Position data of various construction machines under management are periodically reported to the management server. In case a construction machine is found to be located outside a proper working area, it is presumed that a theft has occurred to that machine and a command signal is dispatched from the management side for cutting off power supply to an engine starter motor, stopping the engine of the machine by cutting off fuel supply or taking other suitable measures to prevent construction machine thefts.
By the way, at a working site, except for special cases, normally a construction machine is not put in operation 24 hours a day. Namely, it is usually the case that a construction machine is operated only in a limited time zone of a day and put at rest at night. Throughout the rest time zone at night, a construction machine is stopped on a predetermined place with or without a night guard. Even if a night guard is stationed, it is difficult to keep a machine constantly under strict surveillance. Maybe most of construction machine thefts can be prevented by increasing the number of guards, but from the standpoint of personnel costs it is impractical to increase the number of guards to a sufficient degree.
Constant surveillance of construction machines at respective working sites, including rest periods at night, can be an effective measure for preventing machine thefts or for quickly finding machine thefts. However, since data of locations of respective construction machines have to be acquired via communication satellites, constantly connected surveillance will require vast communication costs. In addition, there will arise another problem that batteries on the respective construction machines are consumed markedly because have to be constantly kept on. Therefore, in a rest period, it is the usual practice to acquire data of construction machine locations at time intervals of one to several hours. If a construction machine theft takes place immediately after acquisition of location data, detection of the machine theft can be delayed for several hours to make it difficult to get the machine back in an early stage.
Normally, a transportation means such as trailer or the like is used for transporting a construction machine like a hydraulic power shovel from one place to another, and the automotive base carrier of the construction machine is put in travel at the time of getting machine onto a transportation means. Similarly, the machine engine has to be started to move the construction machine in the case of a machine theft as well.